/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * We keep our own copy of this algorithm for 2 main reasons:
 *      1. If we didn't, anyone modifying common/os/compress.c would
 *         directly break our on disk format
 *      2. Our version of lzjb does not have a number of checks that the
 *         common/os version needs and uses
 * In particular, we are adding the "feature" that compress() can
 * take a destination buffer size and return -1 if the data will not
 * compress to d_len or less.
 */

#define MATCH_BITS      6
#define MATCH_MIN       3
#define MATCH_MAX       ((1 << MATCH_BITS) + (MATCH_MIN - 1))
#define OFFSET_MASK     ((1 << (16 - MATCH_BITS)) - 1)
#define LEMPEL_SIZE     256

/*ARGSUSED*/
static int
lzjb_decompress(void *s_start, void *d_start, size_t s_len __unused,
    size_t d_len, int n __unused)
{
        unsigned char *src = s_start;
        unsigned char *dst = d_start;
        unsigned char *d_end = (unsigned char *)d_start + d_len;
        unsigned char *cpy, copymap = 0;
        int copymask = 1 << (NBBY - 1);

        while (dst < d_end) {
                if ((copymask <<= 1) == (1 << NBBY)) {
                        copymask = 1;
                        copymap = *src++;
                }
                if (copymap & copymask) {
                        int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
                        int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
                        src += 2;
                        if ((cpy = dst - offset) < (unsigned char *)d_start)
                                return (-1);
                        while (--mlen >= 0 && dst < d_end)
                                *dst++ = *cpy++;
                } else {
                        *dst++ = *src++;
                }
        }
        return (0);
}